Cardiovascular disease is less common in premenopausal women compared with men of the same age, but dramatically increases in postmenopausal women. Also, experimental data have suggested protective effects of estrogen (E2) on the vascular endothelium by affecting the release of vasodilator factors such as nitric oxide and vasoconstrictive factors such as endothelin-1 (ET-1). ET-1 activates both endothelin A (ETAR) and endothelin B receptors (ETBR). Although the role of ETAR in mediating vasoconstriction and hypertension (HTN) has been studied extensively, the role of ETBR in the regulation of vascular function and blood pressure (BP) particularly in females is not clearly defined. The objective of this proposal is to test the hypothesis that the endothelial ETBR plays a major role in the regulation of vascular function in females. An increase in the expression/activity of ETBR activates endothelium-dependent vascular relaxation pathways, and counteracts the ET- 1/ETAR-mediated vasoconstriction, and thereby provides a vascular protective mechanism against HTN in females. E2-deficient states are associated with decreased endothelial ETBR expression/activity, unbalanced increase in ETAR-mediated vasoconstriction and HTN. Therefore, upregulation of ETBR activity enhances the benefits of E2 replacement on BP and vascular function in E2-deficient females. To test this hypothesis experiments will be conducted on intact males, as well as intact, ovariectomized (OVX) female, and E2-replaced OVX female Sprague-Dawley rats. The specific aims are to determine: 1) Whether the decreased BP in females reflects an upregulation of endothelial ETBR expression/activity and activation of ETBR-mediated nitric oxide (NO)-cGMP, prostacyclin (PGI2)-cAMP and hyperpolarizing factor (EDHF) vascular relaxation pathways. 2) Whether E2 deficiency in females is associated with increased BP due to downregulation of ETBR expression/activity, and unbalanced activation of ETAR-mediated [Ca2+]I, protein kinase C (PKC) and Rho-kinase pathways of vascular smooth muscle (VSM) contraction. 3) Whether upregulation of ETBR activity enhances the beneficial effects of E2 replacement on BP and vascular function in E2- deficient females. The results from these exploratory studies should help to define better the ETBR- mediated vascular protective mechanisms in females. The studies will also shed light on the potential benefits of ETBR upregulation as a complementary approach to enhance the vascular benefits of E2 replacement on the vasoconstriction and HTN associated with E2 deficiency in menopausal women. PUBLIC HEALTH RELEVANCE: Sex differences in the prevalence of cardiovascular disease have been suggested. The objective of this proposal is to investigate whether the endothelin B receptor subtype in the vascular endothelium plays a major role in the sex differences in vascular function, and in protecting against hypertension in females. These studies should help to understand better the vascular protective mechanisms of endothelin B receptors in females, and would shed light on the pathophysiological basis of the increased vascular resistance and hypertension associated with estrogen deficiency in menopausal women.